Gas exchange of oxygen between plasma and hepato-splanchnic interstitial fluid is studied by sampling hepatic and mesenteric lymph and thoracic duct lymph, the latter fluid derived primarily from the liver and extrahepatic portal bed. Data thus far obtained indicate that changes in oxygen tensions in mesenteric, hepatic and thoracic duct lymph provide direct information concerning alterations in exchange of oxygen in splanchnic tissues and provide an on-line monitoring of oxidative metabolism and microcirculatory dynamics in the liver and small intestine in normal and pathologic states. These findings are being pursued to elucidate some of the poorly understood problems of tissue oxygenation in hypovolemic and "septic" shock and in disorders of the liver, heart and digestive tract. BIBLIOGRAPHIC REFERENCES: Witte, C.L. and M.H. Witte: The Circulation in Portal Hypertension. Yale J. Bio. & Med. 48:141, 1975. Witte, C.L., T. Hicks, M.H. Witte, W. Renert, C. Butler: Vascular Spider: A Cutaneous Manifestation of Hyperdynamic Blood Flow in Hepatic Cirrhosis. South. Med. J. 68:246, 1975.